muscle

muscle

[mus´'l]

a bundle of long slender cells (muscle fibers) that have the power to contract and hence to produce movement. Muscles are responsible for locomotion and play an important part in performing vital body functions. They also protect the contents of the abdomen against injury and help support the body. See appendix 3-4 and see color plates.

Muscle fibers range in length from a few hundred thousandths of a centimeter to several centimeters. They also vary in shape, and in color from white to deep red. Each fiber receives its own nerve impulses, so that fine and varied motions are possible. Each has its small stored supply of glycogen, which it uses as fuel for energy. Muscles, especially the heart, also use free fatty acids as fuel. At the signal of an impulse traveling down the nerve, the muscle fiber changes chemical energy into mechanical energy, and the result is muscle contraction.

Some muscles are attached to bones by tendons. Others are attached to other muscles, or to skin (producing the smile, the wink, and other facial expressions, for example). All or part of the walls of hollow internal organs, such as the heart, stomach, intestines, and blood vessels, are composed of muscles. The last stages of swallowing and of peristalsis are actually series of contractions by the muscles in the walls of the organs involved.

Types of Muscle. There are three types of muscle: involuntary, voluntary, and cardiac, composed respectively of smooth, striated, and mixed smooth and striated tissue.

Types and structure of muscle. From Dorland's, 2000.

Involuntary muscles are those not under the control of the conscious part of the brain; they respond to the nerve impulses of the autonomic nervous system. They include the countless short-fibered, or smooth, muscles of the internal organs and power the digestive tract, the pupils of the eyes, and all other involuntary mechanisms.

Voluntary muscles are those controlled by the conscious part of the brain, and are striated. These are the skeletal muscles that enable the body to move, and there are more than 600 of them in the human body. Their fibers are grouped together in sheaths of muscle cells. Groups of fibers are bundled together into fascicles, surrounded by a tough sheet of connective tissue to form a muscle group such as the biceps. Unlike the involuntary muscles, which can remain in a state of contraction for long periods without tiring and are capable of sustained rhythmic contractions, the voluntary muscles are readily subject to fatigue.

Cardiac muscles (the muscles of the heart) are the third kind; they are involuntary and consist of striated fibers different from those of voluntary muscle. The contraction and relaxation of cardiac muscle continues at a rhythmic pace until death unless the muscle is injured in some way.

Voluntary muscles extend from one bone to another, cause movements by contraction, and work on the principle of leverage. For every direct action made by a muscle, an antagonistic muscle can cause an opposite movement. To flex the arm, the biceps contracts and the triceps relaxes; to extend the arm, the triceps contracts and the biceps relaxes.

Physiology of Muscles. No muscle stays completely relaxed, and as long as a person is conscious, it remains slightly contracted. This condition is called tonus, or tone. It keeps the bones in place and enables a posture to be maintained. It allows a person to remain standing, sitting up straight, kneeling, or in any other natural position. Muscles also have elasticity. They are capable of being stretched and of performing reflex actions. This is made possible by the motor and sensory nerves which serve the muscles.

Muscles enable the body to perform different types of movement. Those that bend a limb at a joint, raising a thigh or bending an elbow, are called flexors. Those that straighten a limb are called extensors. Others, the abductors, make possible movement away from the midline of the body, whereas the adductors permit movement toward the midline. Muscles always act in opposing groups. In bending an elbow or flexing a muscle, for example, the biceps (flexor) contracts and the triceps (extensor) relaxes. The reverse happens in straightening the elbow.

A muscle that has contracted many times, and has exhausted its stores of glycogen and other substances, and accumulated too much lactic acid, becomes unable to contract further and suffers from fatigue. In prolonged exhausting work, fat in the muscles can also be used for energy, and as a consequence the muscles become leaner.

articular muscle one that has one end attached to the capsule of a joint.

auricular m's

1. the extrinsic auricular muscles, including the anterior, posterior, and superior auricular muscles. See appendix 3-4.

2. the intrinsic auricular muscles that extend from one part of the auricle to another, including the helicis major, helicis minor, tragicus, antitragicus, transverse auricular, and oblique auricular muscles. See appendix 3-4.

cruciate muscle a muscle in which the fiber bundles are arranged in the shape of an X.

cutaneous muscle striated muscle that inserts into the skin.

deltoid muscle the muscular cap of the shoulder, often used as a site for an intramuscular injection. See appendix 3-4.

extraocular m's the six voluntary muscles that move the eyeball: superior, inferior, middle, and lateral recti, and superior and inferior oblique muscles. See appendix 3-4.

extrinsic muscle one that originates in another part than that of its insertion, as those originating outside the eye, which move the eyeball.

gluteal m's three muscles, the greatest, middle, and least, that extend, abduct, and rotate the thigh. See appendix 3-4.

hamstring m's the muscles of the back of the thigh, including the biceps femoris, semitendinosus, and semimembranosus. See appendix 3-4.

intraocular m's the intrinsic muscles of the eyeball. See appendix 3-4.

intrinsic muscle one whose origin and insertion are both in the same part or organ, as those entirely within the eye.

multipennate muscle a muscle in which the fiber bundles converge to several tendons.

palatine m's the intrinsic and extrinsic muscles that act upon the soft palate.

pectoral m's four muscles of the chest; See appendix 3-4.

quadrate muscle a square-shaped muscle; see appendix 3-4.

quadriceps muscle a name applied collectively to four muscles of the thigh; see anatomic Table of Muscles in the Appendices.

scalene m's four muscles of the upper thorax that raise the first two ribs, aiding in respiration. See appendix 3-4.

skeletal m's striated muscles that are attached to bones and typically cross at least one joint.

sphincter muscle a ringlike muscle that closes a natural orifice; called also sphincter.

synergic m's (synergistic m's) those that assist one another in action.

thenar m's the abductor and flexor muscles of the thumb. See appendix 3-4.

triangular muscle a muscle that is triangular in shape.

yoked m's those that normally act simultaneously and equally, as in moving the eyes.

mus·cle

(mŭs'ĕl), [TA]

A primary tissue, consisting predominantly of highly specialized contractile cells, which may be classified as skeletal muscle, cardiac muscle, or smooth muscle; microscopically, the latter is lacking in transverse striations characteristic of the other two types; one of the contractile organs of the body by which movements of the various organs and parts are effected; typical muscle is a mass of musculus fibers (venter or belly), attached at each extremity, by means of a tendon, to a bone or other structure; the more proximal or more fixed attachment is called the origin (q.v.), the more distal or more movable attachment is the insertion (q.v.); the narrowing part of the belly that is attached to the tendon of origin is called the caput or head. For gross anatomic description, see musculus

1. the extrinsic auricular muscles, including the anterior, posterior, and superior auricular muscles.

2. the intrinsic auricular muscles that extend from one part of the auricle to another, including the helicis major, helicis minor, tragicus, antitragicus, transverse auricular, and oblique auricular muscles.

constrictor muscle of pharynx, inferiororigin, undersurfaces of cricoid and thyroid cartilages; insertion, median raphe of posterior wall of pharynx; innervation, glossopharyngeal, pharyngeal plexus, and external and recurrent laryngeal; action, constricts pharynx. It is divided into a cricopharyngeal part and a thyropharyngeal part.

constrictor muscle of pharynx, middleorigin, cornua of hyoid and stylohyoid ligament; insertion, median raphe of posterior wall of pharynx; innervation, pharyngeal plexus of vagus and glossopharyngeal; action, constricts pharynx. It is divided into a ceratopharyngeal part and an chondropharyngeal part.

detrusor muscle of bladder , detrusor urinae muscle the bundles of smooth muscle fibers forming the muscular coat of the urinary bladder, which are arranged in a longitudinal and a circular layer and, on contraction, serve to expel urine.

dilator muscle of pupil a name applied to fibers extending radially from the sphincter of pupil to the ciliary margin; innervation, sympathetic; action, dilates iris.

epicranial muscle a name given the muscular covering of the scalp, including the occipitofrontal and temporoparietal muscles, and the galea aponeurotica.

erector muscle of spine a name given the fibers of the more superficial of the deep muscles of the back, originating from the sacrum, spines of the lumbar and the eleventh and twelfth thoracic vertebrae, and the iliac crest, which split and insert as the iliocostal, longissimus, and spinal muscles.

muscles of expression a group of cutaneous muscles of the facial structures, including the muscles of the scalp, ear, eyelids, nose, and mouth, and the platysma.

iliococcygeus muscle the posterior portion of the levator ani which originates as far anteriorly as the obturator canal and inserts on the side of the coccyx and the anococcygeal body; innervation, third and fourth sacral; action, helps to support pelvic viscera and resist increases in intra-abdominal pressure.

iliocostal muscle the lateral division of the erector muscle of spine.

intertransverse muscles small muscles passing between the transverse processes of contiguous vertebrae, including the lateral and medial intertransverse muscles of the loins, the intertransverse muscles of the thorax, and the anterior and posterior intertransverse muscles of the neck.

levator ani muscle a name applied collectively to important muscular components of the pelvic diaphragm, arising mainly from the back of the body of pubis and running backward toward the coccyx, including the pubococcygeus (levator muscle of prostate in male and pubovaginal in female), puborectal, and iliococcygeus muscles.

levator muscle of prostate a part of the anterior portion of the pubococcygeus muscle, inserted in the prostate and the tendinous center of the perineum; innervated by sacral and pudendal nerves, it supports and compresses the prostate and is involved in control of micturition.

levator muscles of ribs originating from the transverse processes of the seventh cervical and first to eleventh thoracic vertebrae and inserting medial to the angle of a lower rib; innervated by intercostal nerves and aiding in elevation of the ribs in respiration.

omohyoid muscle a muscle comprising two bellies (superior and inferior) connected by a central tendon that is bound to the clavicle by a fibrous expansion of the cervical fascia; origin, superior border of scapula; insertion, lateral border of hyoid bone; innervation, upper cervical through ansa cervicalis; action, depresses hyoid bone.

orbicular muscle of mouth a name applied to a complicated sphincter muscle of mouth, comprising a labial part, fibers restricted to the lips, and a marginal part, fibers blending with those of adjacent muscles; innervation, facial; action, closes and protrudes lips.

papillary muscles conical muscular projections from the walls of the cardiac ventricles, attached to the cusps of the atrioventricular valves by the chordae tendineae. There is an anterior and a posterior papillary muscle in each ventricle, as well as a group of small papillary muscles on the septum in the right ventricle.

pectinate muscles a name applied to small ridges of muscle fibers projecting from the inner walls of the auricles of the heart, and extending in the right atrium from the auricle to the crista terminalis.

pubococcygeus muscle the anterior portion of the levator ani muscle, originating anterior to the obturator canal; insertion, anococcygeal ligament and side of coccyx; innervation, third and fourth sacral; action, helps support pelvic viscera and resist increases in intra-abdominal pressure.

puboprostatic muscle smooth muscle fibers contained within the medial puboprostatic ligament, which pass from the prostate anteriorly to the pubic bone.

puborectal muscle a portion of the levator ani muscle having a more lateral origin from the pubic bone, and continuous posteriorly with the corresponding muscle of the opposite side; innervation, third and fourth sacral; action, helps support pelvic viscera and resist increases in intra-abdominal pressure.

pubovaginal muscle a part of the anterior portion of the pubococcygeus muscle, which is inserted into the urethra and vagina; innervated by the sacral and pudendal nerves, it is involved in control of micturition.

pubovesical muscle smooth muscle fibers extending from the neck of the urinary bladder to the pubis.

quadriceps muscle of thigh a name applied collectively to the rectus muscle of thigh and the intermediate, lateral, and medial vastus muscles, inserting by a common tendon that surrounds the patella and ends on the tuberosity of the tibia, and acting to extend the leg upon the thigh.

rectococcygeus muscle smooth muscle fibers originating on the anterior surface of the second and third coccygeal vertebrae and inserting on the posterior surface of the rectum, innervated by autonomic nerves, and acting to retract and elevate the rectum.

rectourethral muscles bands of smooth muscle fibers extending from the perineal flexure of the rectum to the membranous urethra in the male.

rectouterine muscle a band of fibers running between the cervix of the uterus and the rectum, in the rectouterine fold.

rectovesical muscle a band of fibers in the male, connecting the longitudinal musculature of the rectum with the external muscular coat of the bladder.

rotator muscles a series of small muscles deep in the groove between the spinous and transverse processes of the vertebrae; innervation, spinal; action, extend and rotate vertebral column toward opposite side.

Ruysch's muscle the muscular tissue of the fundus uteri.

sacrococcygeal muscle, anterior a musculotendinous slip passing from the lower sacral vertebrae to the coccyx.

sacrococcygeal muscle, posterior a muscular slip passing from the posterior aspect of the sacrum to the coccyx.

sphincter muscle of urethra, internal , sphincter muscle of urinary bladder a circular layer of smooth muscle fibers surrounding the internal urethral orifice in males, innervated by the vesical nerve, and acting to close the internal orifice of the urethra. No such structure exists in females.

splenius muscle of neckorigin, spinous processes of third to sixth thoracic vertebrae; insertion, transverse processes of two or three upper cervical vertebrae; innervation, dorsal branches of lower cervical; action, extends, rotates head and neck.

muscle

1. A tissue composed of fibers capable of contracting to effect bodily movement.

2. A contractile organ consisting of a special bundle of muscle tissue, which moves a particular bone, part, or substance of the body: the heart muscle; the muscles of the arm.

3. Muscular strength: enough muscle to be a high jumper.

mus′cly adj.

muscle (m)

[mus′əl]

Etymology: L, musculus

a kind of tissue composed of fibers or cells that is able to contract, causing movement of body parts and organs. Muscle fibers are richly vascular, excitable, conductive, and elastic. There are two basic kinds-striated muscle and smooth muscle. Striated muscle, which composes all skeletal muscles except the myocardium, is long and voluntary. It responds very quickly to stimulation and is paralyzed by interruption of its innervation. Smooth muscle, of which all visceral muscles are composed, is short and involuntary. It reacts slowly to all stimuli and does not entirely lose its tone if innervation is interrupted. The myocardium is sometimes classified as a third (cardiac) kind of muscle, but it is basically a striated muscle that does not contract as quickly as the striated muscles of the rest of the body. See also cardiac muscle.

MUSCLE

Abbreviation for:Multi Station Clinical Examination (OSCE)

mus·cle

(mŭs'ĕl) [TA]

A primary tissue, consisting predominantly of highly specialized contractile cells, which may be classified as skeletal muscle, cardiac muscle, or smooth muscle; microscopically, the latter is lacking in transverse striations characteristic of the other two types; one of the contractile organs of the body by which movements of the various organs and parts are effected; typical muscle is a mass of muscle fibers (venter or belly), attached at each extremity, by means of a tendon, to a bone or other structure; the more proximal or more fixed attachment is called the origin, the more distal or more movable attachment is the insertion; the narrowing part of the belly that is attached to the tendon of origin is called the caput or head. Synonym(s): musculus.

[L. musculus]

muscle

(mus'el ) [L. musculus, diminutive of mus, mouse]

MORPHOLOGICAL FORMS OF MUSCLE

MORPHOLOGICAL FORMS OF MUSCLE

MORPHOLOGICAL FORMS OF MUSCLE

MORPHOLOGICAL FORMS OF MUSCLE

MORPHOLOGICAL FORMS OF MUSCLE

MORPHOLOGICAL FORMS OF MUSCLE

A type of tissue composed of contractile cells. Each muscle cell is filled with parallel actin and myosin filaments. When activated by an internal release of calcium, the filaments use the energy in ATP to crawl along each other in opposite directions. This movement shortens the length of the cell, which then contracts.

The three general classes of muscle cells (myocytes) are skeletal (striated), cardiac (striated), and smooth; most of the muscle in humans is skeletal. A typical muscle has a central portion called the belly and two or more attachment ends with tendons; the more stationary of the attachments is called the muscle's origin, while the more movable attachment is called the muscle's insertion. See: illustration

adductor muscle

adductor brevis muscle

A muscle of the medial thigh originating on the ramus of the pubis and inserted in the linea aspera of the femur. It adducts, flexes, and medially rotates the thigh and is controlled by the obturator nerve.

agonist muscle

Controlled movements involve two opposing muscles: the agonist muscle produces the main action, while the antagonist muscle produces the opposite action to a lesser degree. The balance between agonist and antagonist muscles allows precise control of the final action.

Synonym: antagonist muscle See: PNF Stretching Techniques

anconeus muscle

A short muscle along the back of and outside the elbow. It originates from the lateral epicondyle of the humerus, crosses the back of the elbow joint on the same side, attaches to the lateral surface of the olecranon process and the adjacent surface of the ulna. It extends the forearm and abducts the elbow as the forearm pronates. It is innervated by the radial nerve (C7, C8, T1).

cardiac muscle

A tissue composed of mitochondrion-filled muscle cells that also contain neatly packed actin and myosin filaments; the filaments are arranged in cylindrical bundles called myofibrils. In each cell, the myofibrils are all aligned in the same direction and are parceled into longitudinal blocks (called sarcomeres) of similar lengths. Under the microscope, the ends of the blocks appear as lines, making cardiac muscle cells appear to have regularly arranged striations. In the muscle tissue, the cardiac muscle cells are connected in branching networks.

Cardiac muscle is innervated by both sympathetic and parasympathetic autonomic motor axons. In addition, cardiac muscle: is stimulated by blood—borne molecules, can conduct electrical impulses from cell to cell, and can independently generate rhythmical contractions. Cardiac muscle, which is found only in the heart, cannot be controlled consciously.

cricothyroid muscle

deep neck muscle

One of the various neck muscles that surround the vertebral column and base of the skull and which are contained in the prevertebral cylinder of deep cervical fascia. All these muscles are innervated by cervical spinal nerves, and most of these muscles act primarily to move and stabilize the head.

deltoid muscle

Shoulder muscle. Origin: a bony ellipse from the lateral third of the clavicle over the acromial process and along the spine of the scapula. Insertion: deltoid tuberosity on the lateral shaft of the humerus. Nerve: axillary (C5-C6). Action: abducts arm.

erector spinae muscle

Three adjacent vertical bands of deep back muscles -- the iliocostalis, longissimus, and spinalis muscles. Origins: a wide tendon running along the iliac crest to the sacrum, the lower lumbar and sacral spinous processes. Insertions: along the back in the angles of the lower ribs, transverse processes of the thoracic and cervical vertebrae. Nerves: dorsal rami of the spinal nerves. Actions: extends (bends backward) the vertebral column and neck, twists the back.

extensor hallucis longus muscle

external intercostal muscles

The outer layer of muscles between the ribs, originating on the lower margin of each rib and inserted on the upper margin of the next rib. During inspiration, they draw adjacent ribs together, pulling them upward and outward, and increasing the volume of the chest cavity. They are controlled by the intercostal nerves.

flexor hallucis longus muscle

flexor pollicis brevis muscle

A muscle of the hand originating on the flexor retinaculum and trapezium, trapezoid, and capitate and inserted on the lateral side of the base of the first phalanx of the thumb. It flexes the thumb at both the carpometacarpal joint and the metacarpophalangeal joint and is controlled by the median and the ulnar nerves.

gemellus muscle

Either of the two muscles that attach to the medial surface of the greater trochanter of the femur (the trochanteric fossa) where they mesh with the tendon of the obturator internus muscle. The superior gemellus muscle arises from the ischial spine and is innervated by the nerve to the obturator internus; the inferior arises from the ischial tuberosity and is innervated by the femoral nerve. Both muscles hold the head of the femur in the acetabulum, rotate (laterally) the thigh in extension, and abduct the thigh when it is flexed.

gracilis muscle

hamstring muscles

Posterior thigh muscles that originate on the ischial tuberosity and act across both the hip and knee joints; they are the biceps femoris, gracilis, sartorius, semitendinosus, and semimembranosus muscles.

infraspinatus muscle

internal intercostal muscles

The muscles between the ribs, lying beneath the external intercostals. During expiration, they pull the ribs downward and inward, decreasing the volume of the chest cavity and contributing to a forced exhalation.

mastication muscle

The chewing muscle, which is innervated by the mandibular division of the trigeminal nerve (CN V). These muscles include the masseter, temporalis, and medial and lateral pterygoid muscles. Synonym: chewing muscle

nonstriated muscle

obturator muscle

Either of the two muscles on each side of the pelvic region that rotate the thighs outward.

opponens pollicis muscle

A muscle of the hand originating on the trapezium and flexor retinaculum and inserted in the first metacarpal. It flexes and adducts the thumb (brings it across the palm) and is controlled by the median nerve.

shoulder muscles

skeletal muscle

A tissue composed of muscle cells (often multinucleated) that contain neatly packed actin and myosin filaments; these filaments are arranged in cylindrical bundles called myofibrils. In each cell, the myofibrils are all aligned in the same direction and are parceled into longitudinal blocks (called sarcomeres) of similar lengths. Under the microscope, the ends of the blocks look like lines, making skeletal muscle cells appear to have regularly arranged striations. See: illustration

Skeletal muscle is innervated by somatic (as opposed to autonomic) motor axons at a synaptic structure called a motor endplate, where acetylcholine is the neurotransmitter. Most skeletal muscles can be controlled consciously, and skeletal muscle is sometimes referred to as voluntary muscle. Skeletal muscle cells contract more forcefully than smooth or cardiac muscle cells.

Skeletal muscle got its name because it usually attaches at one end to bone. Skeletal muscle is by far the most common type of muscle in the body and it plays a major role in normal metabolism, e.g., after a meal, excess glucose is removed from the blood stream primarily by skeletal muscle.

smooth muscle

A tissue composed of muscle cells that contain loosely-organized actin and myosin filaments. The lack of tight organization means that smooth muscle cells do not appear striated when examined under a microscope. Smooth muscle tissue tends to occur as sheets and is typically found in the walls of tubes, e.g., arteries, and sacs, e.g., the gastrointestinal system.

Smooth muscles are innervated by both sympathetic and parasympathetic autonomic motor axons; they are also stimulated by blood-borne molecules. Smooth muscles cannot be consciously controlled, and this form of muscle tissue is called involuntary muscle. Smooth muscle cells contract more slowly than skeletal or cardiac muscle cells.

tibialis posterior muscle

tonic muscle

Skeletal muscle fibers that contract slowly and that cannot propagate an action potential along their cell membranes. Tonic muscles are uncommon in humans and are found only in the extraocular muscles, stapedius muscle, and intrafusal fibers of the muscle spindles. The remainder of human skeletal muscle contains only twitch fibers.

triceps brachii muscle

tricipital muscle

A muscle with three tendons of origin and a single, common insertion.

twitch muscle

Muscle fibers that can conduct axon potentials along their cell membranes. Almost all skeletal muscle in humans is twitch muscle. A very small number of muscles in humans are tonic muscles. Twitch muscles cells can be categorized into a number of types on the basis of the biochemical cycle that they use to produce their energy: red (oxidative), white (glycolytic), or intermediate (oxidative/glycolytic). Most human muscles are composed of a mix of twitch muscle cell types.

unipennate muscle

A muscle whose fibers converge on only one side of a tendon. See: bipennate muscle for illus.

voluntary muscle

A muscle that can be controlled voluntarily; most skeletal muscles are voluntary.

Smooth

Cardiac

Striated

Synonyms

Involuntary

Myocardial

Voluntary

Nonstriated

Skeletal

Visceral

Fibers

Length (in/m)

50–200

25,000

Thickness (in/m)

4–8

75

Shape

Spindles

Cylinders

Markings

No striation

Striation

Marked striation

Nuclei

Single

Single

Multiple

Effects of cutting related nerve

Slight

Regulation of heart rate is lost

Complete paralysis

illustration

muscle

A tissue consisting of large numbers of parallel elongated cells with the power of shortening and thickening so as to approximate their ends and effect movement. Up to 50% of the body weight consists of muscle, most being attached to bone in such a way that muscle contraction causes joints to bend (flex) or straighten (extend). Muscle fibres convert chemical energy into mechanical energy. There are three kinds of muscle—striped (striated) or voluntary muscle; smooth or involuntary muscle occurring in the walls of arteries, the intestines and the urinary tract; and heart muscle (MYOCARDIUM), a network (syncytium) of muscle fibres that contract regularly and automatically without external stimulus.

Fig. 225 Muscle . A sarcomere.

muscle

the fleshy part of any animal that consists of tissue made up of highly contractile cells which serve to move parts of the body relative to each other.

A muscle is composed of many fibres or muscle cells. In STRIATED MUSCLE, each cell contains a bundle of MYOFIBRILS each exhibiting a banding pattern and being made up of a number of SARCOMERES arranged end to end. The sarcomere is the unit of contraction and the banding visible over its surface results from the longitudal filaments which make up the myofibril being of two types, thick (dark) and thin (light). These filaments overlap as shown in Fig. 225. The thick filaments are composed of the protein MYOSIN and the thin filaments of ACTIN. H.E. Huxley and K. Harrison found that on contraction, the light zones (I-BANDS) were comparatively narrow; on relaxation of the muscle the I-bands were broad. Where very strong contraction takes place the H-zone disappears and the thin filaments overlap.

Huxley and Harrison proposed the sliding filament hypothesis, to account for their observations. Bridges occur between thick and thin filaments and in contraction the bridges pull thin filaments past the thick ones using a ratchet mechanism. Some filaments are retained in this ‘pulled past’ position whilst others detach then reattach and repeat the ‘pulling past’ action. ACTOMYSIN is formed at the point of contact of bridge and thin filament. For each bridge to go through its cycle of attachment, contraction and reattachment, the splitting of one molecule of ATP is required, the cycles occurring between 50 and 100 times per second. The supply of ATP comes from MITOCHONDRIA between the fibrils. Calcium ions are released from vesicles in the sarcoplasmic reticulum, by the ACTION POTENTIAL passing along the surface of the fibre and these split the ATP. Troponin activated by the calcium displaces tropomyosin, which prevents myosin bridges from binding with actin fibrils. Once binding takes place this activates ATPase and on hydrolysis of ATP the bridge goes through its cycle of movement.

Figure 1: Muscles of the back.

Figure 2: Muscles of the abdominal wall. Superficial layer shown on the right side of the body, deeper layer on the left.

muscle

contractile soft tissue, responsible for all significant active movements and force-generations in an animal body. Divisible into three classes: (1) skeletal or voluntary muscle the class of muscle acting, in almost all body locations, to move one bone relative to another, the more superficial skeletal muscles being visible under the skin in all but the most obese subjects; (2) cardiac muscle the type unique to the heart; (3) smooth muscle composing the actively adjustable components of the walls of blood vessels and of the gastrointestinal, respiratory, urinary and reproductive tracts. Skeletal and cardiac are the striated muscles; cardiac and smooth share the property of being involuntary. See alsomuscle fibres, muscle fibre types, myofibrils; Figure 1, Figure 2, Figure 3, Figure 4, Figure 5, Figure 6, Figure 7.

Anterior upper femur and tendon of adductor magnusAnterior and lateral surfaces of body of femurGreater trochanter and linea aspera of femurLinea asperaLateral condyle of femur

Superior and medial surfaces of patella and capsule of knee jointSuperior surface of patella and suprapatellar bursaSuperior and lateral surfaces of patella and capsule of knee jointHead of fibulaPosterior surface of upper tibia

Lateral surface of upper two-thirds of lateral fibulaLateral surface of lower two-thirds of lateral fibulaLateral surface of upper one-half of tibia and local interosseous membraneUpper one-half of tibia, fibula and local interosseous membraneAnterior surface of distal one-quarter of fibula

Base of first metatarsal and lateral side of medial (first) cuneiformBase of fifth metatarsalBase of first metatarsal and inferomedial aspect of medial (first) cuneiformMedial (first) cuneiform, inferior aspects of all tarsal bones (except the talus) and bases of second, third and fourth metatarsalsDorsal shaft of fifth metatarsal

Superior and anterior surfaces of the calcaneumMedial process of calcaneal tuberosityPlantar, medial and lateral aspects of calcaneumMedial process of calcaneal tuberosity and flexor retinaculumCalcaneal tuberosity

Dorsum of proximal phalanx of hallux, and extensor expansions of toes 2-4Plantar, middle phalanges of toes 2-5Tendon flexor digitorum longusMedial side of proximal phalanx of halluxLateral side of proximal phalanx of fifth toe

Lateral side of toes 2-4 and medial side toe 2Medial sides of bases of proximal phalanges of toes 3-5Extensor expansions toes 2-5Medial and lateral sides of base of proximal phalanx of halluxLateral side of base of proximal side of halluxLateral side of base of proximal phalanx of toe 5

Table 2: Movements occurring about the joints of the lower limb and foot

Note: Primary action of muscles is printed in normal type; muscles that give some contribution to this action are printed in italics .

The nerve supply to the lower limb (lower leg and foot) is derived from the sciatic and femoral nerves. Dysfunction or compromise of either of these nerves causes marked motor, sensory and autonomic effects in the lower leg and foot.

MTPJ, metatarsophalangeal joint; IPJ, interphalangeal joint.

muscle

A contractile organ of the body which produces movements of the various parts or organs. Typically it is a mass of fleshy tissue, attached at each extremity by means of a tendon to a bone or other structure. Muscles are classified according to structure as non-striated (or unstriated or unstriped or smooth) or striated (or striped), by control as voluntary or involuntary, or by location as cardiac, skeletal or visceral.abducens muscleSeelateral rectus muscle.adducens muscleSeemedial rectus muscle.agonistic muscle A muscle that performs the desired movement, or does the opposite to an antagonistic muscle. Example: the left lateral rectus is the agonistic muscle when the left eye turns to the left. Seeantagonistic muscle.antagonistic muscle A muscle that opposes the action of another. Example: the right superior rectus muscle is the contralateral antagonist of the left superior oblique. Seeagonistic muscle; synergistic muscles.Brücke's muscleSeeciliary muscle.ciliary muscle The smooth (unstriated and involuntary) muscle of the ciliary body. In a meridional section of the eye it has the form of a right-angled triangle, the right angle being internal and facing the ciliary processes. The posterior angle is acute and points to the choroid, the hypotenuse runs parallel with the sclera. Some of its fibres have their origin in the scleral spur at the angle of the anterior chamber, while other fibres take origin in the trabecular meshwork. The fibres radiate backward in three directions: (1) Fibres coursing meridionally or longitudinally more or less parallel to the sclera and can be traced posteriorly into the suprachoroid to the equator or even beyond. They end usually in branched stellate figures known as muscle stars with three or more rays to each. These fibres represent Brücke's muscle. (2) Other fibres course radially. These fibres lie deep in the longitudinal fibres from which they are distinguished by the reticular character of their stroma but are often very difficult to separate from the circular fibres. (3) The circular fibres (Müller's muscle) occupy the anterior and inner portion of the ciliary body and run parallel to the limbus. As a whole, these fibres form a ring.Innervation to the ciliary muscle (mainly parasympathetic fibres derived from the oculomotor nerve) is provided through the short ciliary nerves and stimulation causes a contraction of the muscle. However, a small amount of sympathetic supply is also believed to act and relax the muscle. Blood supply to the ciliary muscle is provided by the anterior and long posterior ciliary arteries. Contraction of the ciliary muscle causes a reduction in its length thus causing the whole muscle to move forward and inward. Consequently the zonule of Zinn, which suspends the lens, relaxes. This leads to a decrease in the tension in the capsule of the lens allowing it to become more convex and thereby providing accommodation. Syn. Bowman's muscle. Seemechanism of accommodation; adrenergic receptors; ciliary body; scleral spur; Helmholtz's of accommodation theory; zonule of Zinn.muscle cone A structure formed by the sheath of the four recti muscles as they pass forward from their common origin at the apex of the orbit in the fibrous ring called the annulus of Zinn (and around the optic nerve) to be inserted into the sclera around the eyeball. Some authors consider the muscle cone to include the superior oblique muscle. Seeannulus of Zinn.dilator pupillae muscle Smooth (unstriated and involuntary) muscle whose fibres constitute the posterior membrane of the iris. This muscle extends from the ciliary body close to the margin of the iris where it fuses with the sphincter pupillae muscle. Contraction of the dilator pupillae muscle draws the pupillary margin towards the ciliary body and therefore dilates the pupil. This muscle is supplied by the sympathetic fibres in the long ciliary nerves and by a few parasympathetic fibres. Seeadrenergic receptors; sphincter pupillae muscle; mydriatic.elevator muscle'sSeeinferior oblique muscle; superior rectus muscle.external rectus muscleSeelateral rectus muscle.extraocular muscle's The striated (voluntary) muscles that control the movements of the eyes. There are six such muscles: four recti muscles (lateral rectus, medial rectus, superior rectus and inferior rectus) which move the eye more or less around the transverse and vertical axes, and two oblique muscles (inferior oblique and superior oblique) which move the eyes obliquely. The muscles are composed of striated fibres of varying length, mostly running parallel to the direction of the muscle and united by fibrous connective tissue. They have a greater ratio of nerve fibres to muscle fibres than other striated muscles of the body. The fibre thickness varies from 3 to 50 μm, although functionally there seem to be two main types of fibres, the fast and the slow fibres. The former are the thickest and probably responsible for the fast movements of the eyes (saccades) and the latter consist of thin fibres. The tendons (bands of connective tissue) at one end of each extraocular muscle are attached to bones. This is the origin of the muscle. At the other end of the muscle the tendon is attached to the eye and this area is called the insertion. The substance proper of the muscle is called the belly. Contraction of a muscle occurs in the direction of its constituent fibres and causes a shortening of the muscle. Consequently the eye turns in a given direction depending upon which extraocular muscle is contracting. Contraction results from nervous impulses arriving at the motor end-plate (the junction between an axon and a striated muscle fibre) of the muscle through one of the ocular motor nerves. This causes a neurotransmitter substance to be discharged in the microscopic gap between the end-plate and a muscle fibre. These muscles also possess specialized receptors called muscle spindles, which are small groups of muscle fibres that are provided with both a sensory and a motor nerve supply. There are between 12 and 50 in each muscle. The muscle spindles provide a constant and continuous monitoring of the degree of tension of the muscle itself. Syn. extrinsic muscles; oculorotary muscles. Seecholinergic; felderstruktur fibres; motor unit; strabismus surgery; motility test; three-step test.extrinsic muscle'sSeeextraocular muscles.eyelid retractor muscle'sSeelevator palpebrae superioris muscle; Müller's palpebral muscles.Horner's muscle A thin layer of fibres that originates behind the lacrimal sac from the upper part of the posterior lacrimal crest (a ridge on the lacrimal bone which borders the fossa for the lacrimal sac). The muscle passes outward and forward and divides into two slips surrounding the canaliculi. It then becomes continuous with the pretarsal portions of the orbicularis muscle of the upper and lower lids and with the muscle of Riolan. Horner's muscle may be involved in tear drainage through action on the lacrimal sac. Syn. pars lacrimalis muscle; tensor tarsi muscle. Seemuscle of Riolan.inferior oblique muscle(IO) One of the extraocular muscles, it takes its origin at the antero-medial corner of the floor of the orbit. It passes underneath the inferior rectus in a backward direction (making an angle of about 50º with the sagittal plane of the eye), then under the lateral rectus to be inserted by the shortest tendon of all extraocular muscles on the posterior, temporal portion of the eyeball, for the most part below the horizontal meridian, some 5 mm away from the optic nerve. It is innervated by the oculomotor nerve and it extorts (main action), elevates and abducts the eyeball when the eye is in the primary position. Combined with the action of the superior rectus muscle, it directs the eye upward (Fig. M15). SeeBielschowsky's head tilt test; three-step test.inferior rectus muscle(IR) This is the shortest of the four recti muscles. It arises from the lower part of the annulus of Zinn, runs forward, downward and outward (making an angle of about 23º with the sagittal plane) and inserts into the inferior portion of the sclera about 6.5 mm from the corneal limbus. It is innervated by the inferior division of the oculomotor nerve and it depresses (main action), adducts and extorts the eyeball when the eye is in the primary position (Fig. M15). Seeannulus of Zinn; Müller's palpebral muscles; Bielschowsky's head tilt test.inferior tarsal muscleSeeMüller's palpebral muscles.internal rectus muscleSeemedial rectus muscle.intraocular muscle's The smooth (unstriated and involuntary) muscles found within the eye. They are the ciliary, the dilator pupillae and the sphincter pupillae muscles. Syn. intrinsic muscles. Seecholinergic.lateral rectus muscle(LR) One of the extraocular muscles, it arises from both the lower and upper parts of the annulus of Zinn which bridge the superior orbital fissure. The muscle passes forward along the lateral wall of the orbit, crosses the tendon of the inferior oblique muscle and inserts into the sclera about 6.9 mm from the corneal limbus. It is innervated by the abducens nerve and it abducts the eyeball when the eye is in the primary position (Fig. M15). Syn. external rectus muscle; abducens muscle. Seeannulus of Zinn; check ligament.levator palpebrae superioris muscle Striated muscle that arises from the under surface of the lesser wing of the sphenoid bone above and in front of the optic canal. It passes forward below the roof of the orbit and above the superior rectus muscle and terminates in a tendinous expansion or aponeurosis (also called levator aponeurosis), which spreads out in a fan-shaped manner so as to occupy the whole breadth of the orbit and thus gives the whole muscle the form of an isosceles triangle. From the inferior surface of the aponeurosis arises a thin sheet of smooth muscle fibres called Müller's palpebral muscle (or superior tarsal muscle) which inserts into the posterior margin of the superior tarsal plate and into the superior fornix of the conjunctiva. These smooth muscle fibres are innervated by sympathetic nerves from the superior cervical sympathetic ganglion and assist in elevating the upper eyelid. The fibres of the aponeurosis are attached to the anterior margin of the superior tarsal plate while some fuse with bundles of the orbicularis oculi muscle to attach to the skin. These latter sets of fibres produce the horizontal skin crease of the upper eyelid. The striated levator aponeurosis is innervated by the superior division of the oculomotor nerve and elevates the upper eyelid. Its antagonist is the orbicularis muscle. Seeorbicularis muscle.medial rectus muscle(MR) One of the extraocular muscles, it arises from the medial part of the annulus of Zinn. It passes forward along the medial wall of the orbit and is inserted into the sclera about 5.5 mm from the corneal limbus. It is innervated by the inferior division of the oculomotor nerve and it adducts the eyeball when the eye is in the primary position (Fig. M15). Syn. internal rectus muscle; adducens muscle. Seeannulus of Zinn; check ligament.Müller's muscleSeeciliary muscle.Müller's palpebral muscle's Smooth muscles of the eyelids. The superior one (also called superior tarsal muscle) originates from the under surface of the levator palpebrae superioris muscle and passes below to insert into the upper margin of the tarsal plate of the upper eyelid. The inferior one (also called inferior tarsal muscle) originates from the muscular fascia covering the inferior rectus muscle. It extends upward and inserts into the bulbar conjunctiva and the lower margin of the tarsal plate of the lower eyelid. Müller's palpebral muscles are innervated by sympathetic fibres and help in lifting the upper eyelid and depressing the lower eyelid. They are sometimes referred to as the eyelid retractors.oculorotary muscle'sSeeextraocular muscles.orbicularis muscle A thin oval sheet of striated muscle that surrounds the palpebral fissure, covers the eyelids and spreads out for some distance onto the temple, forehead and cheek. It consists of three portions: (1) The marginal or ciliary portion (muscle of Riolan). (2) The palpebral portion (also called the pars palpebralis muscle) which is the essential part of the muscle and is confined to the lids and may itself be divided into pretarsal portion whose fibres lie in front of the tarsal plates, and the preseptal portion whose fibres extend from the tarsal plates to the orbital margin. The palpebral portion is used in closing the eye without effort or in reflex blinking. (3) The orbital portion (also called the pars orbitalis muscle) which is found in the eyebrow, the temple, the forehead and the cheek. This portion of the muscle is used to close the eye tightly and the skin of the forehead, temple and cheek is drawn towards the inner side of the orbit. The orbicularis muscle is innervated by the facial nerve. Syn. sphincter oculi muscle. Seeectropion; Horner's muscle; levator palpebrae superiotis muscle; muscle of Riolan; myokymia.pars ciliaris muscleSeemuscle of Riolan.pars lacrimalis muscleSeeHorner's muscle.pars orbitalis muscleSeeorbicularis muscle.pars palpebralis muscleSeeorbicularis muscle.pupillary muscle's The dilator pupillae and the sphincter pupillae muscles.muscle of Riolan The ciliary portion of the orbic-ularis muscle, it consists of very fine striated muscle fibres which lie in the dense tissue of the eyelids near their margin. It is continuous with Horner's muscle and encircles the eyelid margins mainly between the tarsal glands and the eyelash follicles. Its action is to bring the eyelid margins together when the eyes are closed. Syn. pars ciliaris muscle. SeeHorner's muscle; orbicularis muscle.sphincter oculi muscleSeeorbicularis muscle.sphincter pupillae muscle Smooth, circular muscle about 1 mm broad, forming a ring all round the pupillary margin near the posterior surface of the iris. It is innervated by parasympathetic fibres of the oculomotor nerve that synapse in the ciliary ganglion and by a few sympathetic fibres. Its contraction produces a reduction in the diameter of the pupil. Seemiotics; dilator pupillae muscle; pupil light reflex.muscle spindleSeeextraocular muscles.superior oblique muscle(SO) This is the longest and thinnest of the extraocular muscles. It arises above and medial to the optic foramen on the small wing of the sphenoid bone. It passes forward between the roof and medial wall of the orbit to the trochlea (which is in the form of a pulley made of fibrocartilage) located at the front of the orbit where it loops over and turns sharply backward, downward and outward (making an angle of about 55º with the sagittal plane), passes under the superior rectus and inserts into the sclera just behind the equator on the superior temporal portion of the eyeball. It is innervated by the trochlear nerve and it intorts (main action), depresses, and also abducts the eyeball when the eye is in the primary position (Fig. M15). Seetrochlear fossa; Bielschowsky's head tilt test; three-step test.superior rectus muscle(SR) One of the extraocular muscles, it arises from the upper part of the annulus of Zinn. It passes forward and outward (making an angle of about 23º with the sagittal plane) and inserts into the sclera about 7.7 mm from the corneal limbus. It is innervated by the superior division of the oculomotor nerve and elevates (main action), adducts, and also intorts the eyeball when the eye is in the primary position (Fig. M15). Seeannulus of Zinn; Bielschowsky's head tilt test.synergistic muscle's Muscles having a similar and mutually helpful action as, for example, the inferior rectus and superior oblique muscles in depressing the eyeball. SeeTable M5.superior tarsal muscleSeeMüller's palpebral muscles.tarsal muscle'sSeeMüller's palpebral muscles.tensor tarsi muscleSeeHorner's muscle.yoke muscle's Muscles of the two eyes which simultaneously contract to turn the eyes in a given direction. Example: the medial rectus of the right eye and the lateral rectus of the left eye when turning the eyes to the left. SeeHering's law of equal innervation; motility test; version.

Fig. M15 Extraocular muscles of the eye (the left superior rectus muscle is not shown to allow a clearer view of the muscles underneath)

muscle(s),

n an organ that, by cellular contraction, produces the movements of life. The two varieties of muscle structure are striated, which includes all the muscles in which contraction is voluntary and the heart muscle (in which contraction is involuntary), and unstriated, smooth, or organic, which includes all the involuntary muscles (except the heart), such as the muscular layer of the intestines, bladder, and blood vessels. See also each of the individual muscles of the head and neck as they are listed.

muscle, buccinator

(buk´sinātər), n the muscle consisting of three bands and composing the wall of the cheek between the mandible and the maxilla; it causes the cheek to stay tight to the teeth and the lip corners to pull inward. It is often known as the “cheek muscle.”

muscle, ciliary

(sil´ēer´ē), n a tiny smooth muscle at the junction of the cornea and sclera, consisting of two groups of fibers: circular fibers, which exert parasympathetic control through the oculomotor nerve and the ciliary ganglion, and radial fibers, which exert sympathetic control. Ciliary muscles are responsible for accommodation for far vision through flattening of the lens.

muscle, concentric, contraction,

n See contraction, muscle, concentric.

muscle contraction,

n See contraction, muscle.

muscle, digastric

n suprahyoid muscle that helps activate the jaw for mastication and swallowing. It has both an anterior and a posterior belly. See also deglutition; mastication; muscle, hyoid.

muscle, eccentric, contraction,

n See contraction, muscle, eccentric.

muscle, elasticity of, physical,

n the physical quality of being elastic, of yielding to passive physical stretch.

muscle, elasticity of, physiologic,

n the biologic quality, unique for muscle, of being able to change and resume size under neuromuscular control.

muscle fatigue,

n the depletion of the metabolites necessary to sustain or repeat a muscle contraction.

muscle fiber,

n the cell of muscle tissue. The three types of muscle fibers are striated (voluntary), cardiac, and smooth (involuntary).

muscle, functional changes of,

n.pl asymmetric modifications in length, diameter, and bulk of muscle fibers as a result of variations in function. Muscle responds to normal function by maintenance of bulk. An increase in bulk is caused by an increase in the number of capillaries and in the mean diameter of individual muscle fibers. The response to function accounts for the asymmetry of the musculature, which is frequently found when the growth patterns have been influenced by a traumatogenic agent such as disease, injury, or surgery, and also by the functional processes of the body itself, such as posture and habit. Asymmetry is not necessarily pathologic; i.e., it may be the result of differences in habits of chewing, incision, speech sounds, and facial gestures.

muscle, genioglossus

(jē´nēōglôs´us), n an extrinsic tongue muscle that originates from the genial tubercles of the mandible and extends inside the tongue. It aids in tongue extension and prevents respiratory obstruction.

muscle, geniohyoid

(jē´nēōhī´oid), n suprahyoid muscle attached to the superior surface of the hyoid bone. This muscle, which is used for mastication and swallowing, originates on the genial tubercles of the mandible and extends along the floor of the oral cavity. See also deglutition; mastication; muscle, hyoid.

muscle, hyoglossus

(hī´ōglôs´əs), n an extrinsic tongue muscle that originates from the hyoid bone and extends on the lateral surface of the body of the tongue. It depresses the tongue during mastication and speech.

muscle, hypertenseness,

n an increased muscular tension that is not easily released but that does not prevent normal lengthening of the muscle. Hypertenseness is found in patients with general nervousness.

muscle, innervation of, reciprocal,

n a phenomenon of antagonistic muscles demonstrated during a concentric contraction such as that of the temporal muscle. Innervation of the antagonist, the external pterygoid muscle, is partially inhibited, so that freedom of action in flexing the temporomandibular joint is possible. This phenomenon demonstrates inhibition of antagonistic skeletal muscles in a reflex arc brought about automatically by a reduction of the motor discharges from the central nervous system. One of the two muscles in the reflex arc is activated, and the activity of the other is depressed.

muscle, isometric, contraction,

n See contraction, muscle, isometric.

muscle, isotonic, contraction,

n See contraction, muscle, isotonic.

muscle, lateral pterygoid

(lat´ərəl ter´igoid), n the muscle whose superior head attaches to the sphenoid bone and whose inferior head attaches to the pterygoid plate. This muscle moves the jaw from side to side. Also known as the external pterygoid muscle.

muscle, masseter

(məsē´tər), n one of the four muscles of mastication. The thick rectangular muscle in the cheek that functions to close the jaw. The masseter muscle arises from the zygomatic arch and inserts into the mandible at the corner of the jaw.

Palpation of the masseter muscle.

muscle memory,

n a kinesthetic phenomenon by which a muscle or set of muscles may involuntarily produce movement that follows a pattern that has become established by frequent repetition over a long period.

muscle, mentalis

(mental´əs), n the muscle in the chin that originates in the incisive fossa and is inserted into the skin of the chin; it lifts the lower lip and wrinkles the skin of chin.

muscle, mylohyoid,

n suprahyoid muscle originating from the mandible. It helps to raise the tongue and lower the mandible for mastication and swallowing and also forms the floor of the oral cavity. See also deglutition; mastication; muscles, hyoid.

muscle, omohyoid

n infrahyoid muscle with both inferior and superior bellies. It is used for chewing and swallowing. See also muscles, hyoid.

muscle, orbicularis oris

(orbik´yəlar´əs or´is), n the muscle that encircles the oral cavity; it encompasses both fibers proper to the lips as well as the adjacent facial muscles. Also known as the “kissing muscle” for its puckering role, it is intimately involved in the opening and closing of the oral cavity.

muscle, palatoglossal

(pal´ətōglos´əl), n the interior palate muscle that serves to raise and lower the posterior part of the tongue.

muscle, palatopharyngeus

(pal´ətōferin´jēəs), n the muscle that extends from the soft palate to the walls of the laryngopharynx and the thyroid cartilage to form the posterior facial pillars; it is used during swallowing to cover the opening of the nasopharynx by moving the palate and the posterior pharyngeal wall.

muscle, physical characteristics of primary, elasticity,

n.pl a muscle is an elastic body. Its individual fibers follow Hooke's law of elastic bodies: that is, the amount of elongation is proportional to the stretching force. The muscle organs contain tissue other than muscle fibers and thus deviate slightly from this law. The human muscle fiber can contract to about half its total length.

muscle, platysma

(plətiz´mə), n the muscle that extends from the clavicle and shoulder, along the neck, to the mandible and the muscles surrounding the oral cavity; it allows the corners of the oral cavity to be pulled down in a grimace and the skin of the neck to be raised into ridges and depressions.

muscle, regeneration of reproduction or repair of muscle fiber,

n a sequela to many types of muscle damage. Reparation is always associated with the proliferation of sarcolemmic nuclei. Connective tissue elements do not participate in this process except to bridge the gap and offer support for the regenerative fibers. The regenerative process takes place in two forms: regeneration by budding from the surviving parts of the muscle fibers, which occurs when segments of the muscle fiber and its sheath are destroyed, and regeneration by proliferation of cellular bands, which occurs when the sarcolemmic nuclei are spared and can form a sarcoplasmic band by linkage of the cytoplasmic processes.

muscle relaxation,

n the resting state of a muscle fiber or a group of muscle fibers.

muscle reposition,

n surgical replacement of a muscle attachment into a more acceptable functional position.

muscle, sequence of, development,

n the pattern of embryologic muscular development. The muscles of the neck and trunk are the first to develop; they are followed by the lingual and facial musculature and then by the distal and proximal appendicular musculature.

muscle, smooth,

n the simplest of the three types of muscle (smooth, striated, and cardiac). It is the muscle of the lining of the digestive tract, ducts of glands, and viscera associated with the gut. It also supplies the muscles for the genitourinary tract, structures of the blood vessels, connective tissues of the mucous membranes, and skin with its appendages. A typical fiber is a slender, spindle-shaped body averaging a few tenths of a millimeter in length. There is a single, centrally striated nucleus. The cytoplasm appears homogeneous. The cells are arranged in bands, or bundles, with interspersed connective tissue fibers uniting them into an effective common mass. They are innervated in part by nerve fibers and in part by the contraction of adjacent muscle tissues. The digestive tract, particularly, demonstrates waves of contraction that pass along a band of smooth muscle.

muscle, spasticity of,

n increased muscular tension of antagonists that prevents normal movement; caused by an inability to relax (a loss of reciprocal inhibition) resulting from a lesion of the upper motor neuron.

muscle, sternocleidomastoid (SCM),

n a muscle of the neck that is attached to the mastoid process and superior nuchal line and by separate heads to the sternum and clavicle. It functions with other muscles to turn the head from side to side and tilt the head to one side or the other. It separates the neck region into triangles.

muscle, sternothyroid

(stur´nōthī´roid), n infrahyoid mus-cle that runs from the sternum to the thyroid cartilage and depresses the larynx and the thyroid cartilage for mastication and swallowing. See also deglutition; mastication; muscle, hyoid.

muscle, striated

n skeletal muscles forming the bulk of the body; the voluntary muscles derived from the myotomes of the embryo. Generally, they are organized as formed muscles that attach to and move the skeletal structures. The cells are large, elongated, and cylindric, with lengths ranging from 1 mm to several centimeters. The cells have multiple nuclei that are peripherally situated and scattered along the length of the fiber. The fiber contains a large number of elongated fibers that, under the microscope, appear as the alternating light and dark bands that give the characteristic striated appearance of striated muscle. The dimensional relationships between these light and dark bands are altered during contraction of the muscle fiber. The potential interaction between these bands permits the wide range of selective purposeful and rapid activity of the skeletal muscles.

muscle

an organ composed of bundles of fibers that has the power to contract and hence to produce movement. Muscles are responsible for locomotion and help support the body, generate heat and perform a number of other functions. They are of two varieties: striated (or striped, voluntary or skeletal), which makes up most of the meat of a carcass, and smooth (unstriated), which includes all the involuntary muscle of the viscera, heart and blood vessels.

Skeletal muscle fibers range in length from a few millimeters to many centimeters. They also vary in color from white to deep red. Each muscle fiber receives its own nerve impulses, which trigger fine and varied motions. At the signal of an impulse traveling down the nerve, the muscle fiber changes chemical energy into mechanical energy, and the result is muscle contraction. At least two major types of muscle fiber have been identified by histochemical techniques: type I (red) fibers, which have a slow contraction; and type II (white) fibers, which have a fast contraction.

Some muscles are attached to bones by tendons. Others are attached to other muscles, and to skin, producing, for example, the skin twitch, the eye blink and hair erection. Parts of the walls of hollow internal organs, such as the heart, stomach and intestines and also blood vessels, are composed of muscles. See also muscular. For a complete list of named muscles see Table 13.

agonistic muscle

prime mover; a muscle opposed in action by another muscle, called the antagonist.

antagonistic muscle

one that counteracts the action of another muscle (the agonist).

appendicular muscle

one of the muscles of a limb.

arrector pili muscle

small, smooth muscle attached to the bulb of the hair which causes erection of the hair and compression of the attending sebaceous gland when it contracts.

arterial muscle

part of the tunica media; smooth muscle fibers arranged in a circular pattern around the lumen.

the muscle may have torn away from its insertion, in which case the tendon will be slack, or it may be a complete or partial separation of the belly of the muscle, when the muscle will be swollen and hard. Structural and conformational changes may result, e.g. in rupture of the gastrocnemius muscle, and the hernias caused by rupture of the ventral abdominal muscles or the diaphragm.

skeletal m's

striated muscles that are attached to bones and typically cross at least one joint. Called also voluntary or striated muscles.

a relative deficiency of type II muscle fibers, with a predominance of type I fibers. An inherited defect in Labrador retrievers. Clinical signs include stunted growth, and muscle weakness and abnormal gait, which subside with rest, from an early age.

those that normally act simultaneously and equally, as in moving the eyes.

Patient discussion about muscle

Q. What are muscle cramps caused from? I am a 30 year old woman and am pregnant. I keep on getting a muscle cramps on the back on my lower leg. It really hurts! What is causing it and how can I prevent it?

A. You can get muscle cramps almost anywhere in your body during pregnancy, but the most common site is your calves. Although the spasms may only last a short time, they can be very severe.No one knows for certain what causes leg cramps in pregnancy, though there are some theories: Deficiencies in salt, calcium, magnesium and vitamin C or changes in blood circulation. To prevent it make sure to stretch your muscles before bed and if you do get a cramp, immediately stretch your calf muscles: Straighten your leg, heel first, and gently flex your toes back toward your shins. It might hurt at first, but it will ease the spasm and the pain will gradually go away.

A. The idea that lactic acid is what causes muscle burn during exercise is outdated and not supported by the most recent research. Lactic acid is actually a primary source of fuel during anaerobic exercise.

Muscle cells take up glucose (muscle glycogen) and convert them into lactic acid, which the mitrochondria in the cells then use for energy. The old theory was that lactic acid was a waste product that hindered performance. New scholarship on this actually shows that lactic acid is a SOURCE of fuel, not a "dead end as far as energy production is concerned."

Much of this new thinking has come from research performed by Dr. George Brooks at the University of California - Berkely. You can read more here: http://berkeley.edu/news/media/releases/2006/04/19_lactate.shtml

Researchers also now believe that muscle acidosis (that burning sensation during exercise)is not caused by increases in lactate within the muscle, but rather by a completely separate reaction when ATP is h

Q. What can I do to build muscle and develop immunity? I'm Mickey, 21. My height is 5’5” and I weigh 176 lbs. I love out door games especially soccer. I have poor immunity that I get sick very often. What can I do to build muscle and develop immunity?

A. You must keep your GI tract healthy. Eat plenty of soluble and insoluble fiber every day minimum of 25 grams, but gradually shoot up to 35 grams. Include yogurt or encapsulated probiotics in your daily diet. The more robust your GI tract, the more available nutrients such as glutamine is for anabolic muscle metabolism. Another nutrient is ImmunoLin, a purified source of immunoglobin G (IgG), which fights off viruses that may enter the body through the GI tract. Research has shown that IgG not only improves get immune health, which helps you to stay healthy, but also helps people who suffer from various allergies. Do exercise regularly. If you follow the above tips, I am sure you will get the desired results.

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